Cylindrical heating apparatus

ABSTRACT

A specimen heating apparatus includes a heater unit configured to heat a test specimen held in a material testing machine, a heater holding unit configured to hold the heater unit in a set position relative to the test specimen for heating, a specimen temperature measurement unit attached to the heater unit and configured to measure temperature of the test specimen when the heater unit is in the set position, a temperature controller configured to control heating of the heater unit in response to a temperature measured by the specimen temperature measurement unit, and a thermal insulation unit configured to cover the heater unit, wherein the heater holding unit holds the heater unit in such a way that the heater unit is allowed to be brought to and removed from the set position while the test specimen is being held in the material testing machine.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.16/360,648, having a filing date of Mar. 21, 2019.

BACKGROUND Technical Field

The present disclosure is directed to a heating apparatus for heating atest specimen held in a material testing machine. Specifically, thepresent disclosure is directed to an in-situ heating apparatus that canbe used in various universal testing machines.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventor, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

A universal testing machine (UTM), or tensometer, is used to applyvarious types of mechanical tests that help to understand how materialsbehave under different types of load. These different types of loads aretension, compression, cyclic, torsion, shear, and bending. Each testapplied by the UTM provides different aspects of the mechanicalproperties of a material. Different mechanical tests can be fracture,fatigue, creep, wearing, etc. These mechanical tests provide thematerial's characteristic features before failure. The material'scharacteristic features define the material's thresholds prior tofailure. These characteristics are necessary for designers and engineersto ensure safe usage of the materials.

Many previous studies have determined the mechanical characteristics ofmany materials and they are all set in well-known handbook references(i.e., ASM Handbook, “Volume 1,” Properties and Selection: Irons,Steels, and High Performance Alloys, vol. 1, 2005, B. John, B. John, andB. Peter, ASM handbook Volume 8: mechanical testing and evaluation. AsmInternational, 2017). However, the ongoing development of new materialsrequires conducting extensive mechanical tests and defining theirmechanical characteristics to update the handbook references.

In real-world operating conditions, engineering parts and structures mayface different environments, such as high temperatures, cryogenic,onshore, humidity, corrosive, and high pressure. In each environment,engineers and designers require special attention to study theperformance of the materials and reconsider the environmental effects onmetal or composite material life. An example of engineering parts inhigh-temperature environments is gas turbine blades (made of Inconel 718super alloy), operating in temperatures over 1,000° C. (B. Erice and F.Gálvez, “A coupled elastoplastic-damage constitutive model with Lodeangle dependent failure criterion,” International Journal of Solids andStructures, vol. 51, no. 1, pp. 93-110, Jan. 1, 2014, B. Erice, M. J.Pérez-Martin, and F. Gálvez, “An experimental and numerical study ofductile failure under quasi-static and impact loadings of Inconel 718nickel-base superalloy,” International Journal of Impact Engineering,vol. 69, no. 0, pp. 11-24, July 2014.). This present disclosure relatesto the influence of high temperatures on material behavior and life andincludes a description of a new apparatus and method to test materialsunder such high temperatures.

Many extensive ongoing studies and published research have investigatedmaterials' different behavior under a variety of high temperatures. YuanR. et al. (R. Yuan, J. J. Kruzic, X. F. Zhang, L. C. De Jonghe, and R.O. Ritchie, “Ambient to high-temperature fracture toughness and cyclicfatigue behavior in Al-containing silicon carbide ceramics,” ActaMaterialia, vol. 51, no. 20, pp. 6477-6491, 2003) examined siliconcarbide ceramics (ABC-SiC) with different percentages of Al contentunder a very high temperature (1,300° C.). It was found that the fatiguelimit for all materials was less when compared to the fatigue limit at25° C. In another recent study, Al-Alkawi et al. (H. J. M. Al-Alkawi, M.H. Ali, and S. G. Mezban, “Elevated temperature fatigue SN curvebehavior for three different carbon percentage steel alloys,”International Journal of Energy and Environment, vol. 8, no. 4, pp.307-315, 2017) tested three different carbon-based steel alloys (theydiffered in carbon content percentage) to compare and investigate theeffect of carbon content on fatigue life in a moderate high-temperatureenvironment (100° C.). The fatigue results were compared to roomtemperature fatigue life to illustrate the effects of high temperatureon the three materials. The research team found that both fatigue lifeand strength decrease dramatically when increasing the temperature. Inaddition, the fatigue strength of the material with a lower content ofcarbon showed a high resistance to cyclic loading and a negligiblereduction in fatigue strength. The high-temperature effects on the threematerials weakens the fatigue strength and life.

Nogami et al. (S. Nogami, A. Nishimura, E. Wakai, H. Tanigawa, T. Itoh,and A. Hasegawa, “Development of fatigue life evaluation method usingsmall specimen,” Journal of Nuclear Materials, vol. 441, no. 1-3, pp.125-132, 2013) presented a new method to evaluate low-cycle fatigue lifeof small specimens, including the effect of specimen size. The appliedhigh temperature was 550° C. The results of the high temperature effectshow a reduction in the fatigue life by 40-90% when compared to roomtemperature fatigue life. Also, the final fracture stage occurred fasterunder high temperatures. Luis et al. (L. Straβberger, A. Chauhan, T.Gräning, S. Czink, and J. Aktaa, “High-temperature low-cycle fatiguebehavior of novel austenitic ODS steels,” International Journal ofFatigue, vol. 93, pp. 194-200, 2016) investigated a new steel(17Cr13Ni—W) fatigue life under high temperature (650° C.). Theyrevealed a minor change in the fatigue life under high temperature dueto the high content of Cr and Ni.

Another study investigated the effect of high temperature on theAluminum alloy 7055 microstructure, fracture for both longitudinal andtransverse orientations, and anisotropic behavior in the high-cyclefatigue regime at ambient (27° C.) and high temperatures (190° C.) (T.S. Srivatsan, S. Anand, S. Sriram, and V. K. Vasudevan, “The high-cyclefatigue and fracture behavior of aluminum alloy 7055,” Materials Scienceand Engineering: A, vol. 281, no. 1-2, pp. 292-304, 2000.). The resultsshowed a significant reduction (35%) in yield strength and an ultimatetensile strength decrease for both longitudinal and transverseorientations in fracture experiments. Likewise, at high temperatures andhigh cyclic stress amplitudes, the fatigue life of the transverse isshorter when compared with the longitudinal orientations. In the samevein, Choe et al. (H. Choe, D. Chen, J. H. Schneibel, and R. O. Ritchie,“Ambient to high temperature fracture toughness and fatigue-crackpropagation behavior in a Mo-12Si-8.5 B (at. %) intermetallic,”Intermetallics, vol. 9, no. 4, pp. 319-329, 2001) compared thefatigue-crack propagation behavior of 1Mo-12Si-8.5B alloy under room andhigh temperatures. They clearly showed a relatively highcrack-initiation and increasing fracture toughness at 800° C. Inaddition, they discovered that the stress intensity verge for fatiguedue to cycling loading under high temperature increased.

Recent research has investigated the influence of a high-temperatureenvironment on material behavior and service life. In all the research,a variety of heat sources and methods were used to heat materialspecimens during or prior to experiments based on the research needs andtheir facility's capability.

Currently, for high-temperature experiments, the heating systems used inUTMs are in-situ furnaces, such as the MTS Model 653 family of furnaces.This heating system is well known in the market for being reliable andefficient, yet very expensive to purchase. Acquiring such furnacesrequires a great deal of budgeting, special care, and training. Althoughthis furnace serves the purpose, relatively few laboratories, researchcenters, and universities around the world (particularly in developingcountries), can afford to acquire this sophisticated furnace. Inaddition, shipping from the manufacturer (i.e. in the US or Europe) is amajor obstacle for developing countries and rural universities.

Environmental chambers are another heating system used in manyspecialized types of research. They provide a good simulation ofreal-world operating conditions, such as temperature, humidity, andcaustic conditions. However, this apparatus is very complicated, heavy,expensive, and requires special training and spacing. Moreover, it doesnot provide access to the sample during the test for strainmeasurements. This heating system is highly delicate, sophisticated, andrequires special operational training.

Another existing option for heating specimens is the induction heatingsystem. This system is based on the laws of electromagnetism. Theinductor coil part, made of copper, very closely surrounds a metalspecimen with no direct contact. A high-frequency AC current runsthrough the coil. The metal specimen is then heated by the inducedcurrent flow in the metal specimen. This method offers an excellentcombination of speed and consistency. However, the heat generated in themetal specimen due to the induced current flow is not radially uniform.The temperature is high at the specimen's surface and at a minimum inthe specimen's core. Also, the induction heating is not applicable fornon-metallic and non-magnetic materials. Moreover, it is challenging touse during testing and strain measuring.

Joule heating is another heating method used mostly for miniature andnano-specimens. It is done by introducing a DC voltage to the specimen'stwo ends that lead to a current flow. The high-density current flow willmake the specimen heat-up in its minimal area. This method requiresspecial attention and calculation in the design of the specimen toensure that the heating area is located in the intended zone of thespecimen. Also, this heating system requires sophisticated experimentaltools and setup. Moreover, it necessitates basic knowledge in theelectric field to calculate the required experimental temperature. Thismethod is only applicable for metals that allow the flow of electriccurrent unlike composite materials.

These are the primarily known and used heating methods used in UTMtesting experiments and research. Each one has its own pros and consduring the experimental setup and tests. However, a common disadvantageof the heating methods mentioned above is that they all require aconsiderable budget to obtain. Research funding is a significantobstacle for many research centers and universities, particularly fordeveloping countries. This issue prevents them from contributing to theinternational research community who share the same interests. Moreover,the cost of the annex services, such as training, installation,continuous maintenance, and shipping can be prohibitive. It is desirableto provide a new heating apparatus and method that overcome theforegoing cons and yet maintain the foregoing pros of the existingheating systems so that researchers and graduate students can easilycontribute while preserving the best quality experimental set up at lesscost. Such a heating apparatus and method may service a vast communityof mechanical engineers, civil engineers, and researchers who have aninterest in discovering both macro- and micro-mechanical properties ofmetals and composite materials under high temperatures. It also providesmany advantages and benefits over other existing heating methods.

SUMMARY OF THE INVENTION

In an exemplary embodiment, a specimen heating apparatus for a materialtesting machine includes a heater unit configured to heat a testspecimen held in the material testing machine for mechanical strengthtesting, a heater holding unit configured to hold the heater unit in aset position relative to the test specimen for heating the test specimenheld in the material testing machine, a specimen temperature measurementunit attached to the heater unit and configured to measure temperatureof the test specimen when the heater unit is in the set position, atemperature controller configured to control heating of the heater unitin response to a temperature measured by the specimen temperaturemeasurement unit, and a thermal insulation unit configured to cover theheater unit, wherein the heater holding unit holds the heater unit insuch a way that the heater unit is allowed to be brought to and removedfrom the set position while the test specimen is being held in thematerial testing machine.

The foregoing general description of the illustrative embodiment and thefollowing detailed description thereof are merely exemplary aspects ofthe teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram illustrating an exemplary system set-up inwhich a specimen heating apparatus is placed in a set position forheating a test specimen held in a material testing machine, according tocertain embodiments;

FIG. 2 is a schematic perspective view of the specimen heating apparatusaccording to a first embodiment;

FIG. 3 is a partial-sectional view of a heater unit of the specimenheating apparatus according to the first embodiment;

FIG. 4 is a perspective view of the heater unit of the specimen heatingapparatus according to the first embodiment placed for heating a testspecimen held in a material testing machine;

FIG. 5 is a schematic cross-sectional view of the heater unit coveredwith a thermal insulation unit according to the first embodiment, whichis placed for heating a test specimen held in a material testingmachine;

FIG. 6 is a schematic block diagram of a temperature controller of thespecimen heating apparatus according to the first embodiment;

FIG. 7 is a diagram illustrating an exemplary feedback loop for thetemperature controller;

FIG. 8 is a schematic perspective view of a heater unit of a specimenheating apparatus according to a second embodiment;

FIG. 9 is a schematic perspective view of the heater unit of thespecimen heating apparatus according to the second embodiment, which isplaced for heating a test specimen held in a material testing machine;

FIG. 10 is a schematic block diagram of the specimen heating apparatusaccording to the second embodiment; and

FIG. 11 is a schematic cross-sectional view of a specimen heatingapparatus according to a third embodiment, which is placed for heating atest specimen held in a material testing machine.

DETAILED DESCRIPTION

In the drawings, like reference numerals designate identical orcorresponding parts throughout the several views. Further, as usedherein, the words “a,” “an” and the like generally carry a meaning of“one or more,” unless stated otherwise. The drawings are generally drawnto scale unless specified otherwise or illustrating schematic structuresor flowcharts. For purposes of the description hereinafter, the terms“upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”,“bottom”, and derivatives thereof shall relate to the disclosedstructures and methods, as oriented in the drawing figures. Furthermore,the terms “approximately,” “approximate,” “about,” and similar termsgenerally refer to ranges that include the identified value within amargin of 20%, 10%, or preferably 5%, and any values therebetween.

Embodiments of the present disclosure are now described in detail withreference to the drawings.

First Embodiment

A specimen heating apparatus according to the first embodiment isdescribed with reference to FIG. 1 to FIG. 7. FIG. 1 is a schematicdiagram illustrating an exemplary system set-up in which a specimenheating apparatus 100 is placed in a set position for heating a testspecimen 700 held in a material testing machine 800, according tocertain embodiments. The material testing machine 800 illustrated inFIG. 1 is also referred to as a universal testing machine (UTM) that canperform various mechanical tests such as tensile, compression, flexural,fracture, fatigue, torsion, and shear tests on materials and components.

In this example, it is assumed that the material testing machine 800 isperforming a tensile test on the test specimen 700. A load-elongationcurve obtained from this tensile test gives a variety of informationsuch as a stress-strain curve, which serves as basis of design work, andenables to obtain tensile mechanical properties of the material beingtested. The material testing machine 800 may alternatively be asingle-function testing machine that can perform tensile testing on thetest specimen 700.

As illustrated in FIG. 1, the material testing machine 800 includes amain frame 810, a pair of specimen grips 820, and connecting rods 830that connect the main frame 810 and the specimen grips 820. The testspecimen 700 is being held between the specimen grips 820 during tensiletesting. The test specimen 700 is, for example, a round bar made of amaterial to be tested and has two shoulders and a gauge section inbetween. The shoulders are larger and gripped by the specimen grip 820.The gauge section has a smaller cross-section. The test specimen 700 mayalso be prepared in a square cross section along the gauge section.Alternatively, the test specimen 700 may have threaded shoulders. Inthis case, the specimen grip 820 is provided with a threaded grip thatmates with the threaded shoulder of the test specimen 700. In the casewhere the test specimen 700 has threaded shoulders, the length of eachshoulder for gripping may be made shorter, thereby making it possible toreduce the overall length of the test specimen 700.

In the case where the test specimen 700 is made of carbon steel, plasticdeformation occurs when it is heated to 200-500° C. This phenomenon iscalled blue brittleness. To check characteristics of the test specimen700 in such a high temperature environment, it is necessary to perform atensile test on the test specimen 700 while heating the test specimen700. With the specimen heating apparatus 100, it is possible to performa tensile test on the test specimen 700 placed in the material testingmachine 800 at an elevated temperature.

FIG. 2 is a schematic perspective view of the specimen heating apparatus100 according to the first embodiment placed for heating the testspecimen 700 held in the material testing machine 800. The specimenheating apparatus 100 includes a heater unit 200, a specimen temperaturemeasurement unit 300, a temperature controller 400, a heater holdingunit 500, and a thermal insulation unit 600. The specimen temperaturemeasurement unit 300 is not illustrated in FIG. 2 and will be describedin detail below. Further, the thermal insulation unit 600 illustrated inFIG. 2 is in the state before being attached to the heater unit 200.

The heater holding unit 500 is a structure designed in a way that holdsthe heater unit 200 and maintains stability and stiffness to withstandthe weight of the heater unit 200 at high temperature environment. Theheater holding unit 500 is, for example, made of any metal that cancarry the heater unit 200. In the present embodiment, the heater holdingunit 500 includes a heater holding ring 510, a heater holding arm 520, atemperature controller holding arm 530, a vertical stand 540, and asupport base 550. The heater holding ring 510 has a ring-like shape forsecurely holding the heater unit 200. The heater holder ring 510 is, forexample, made of a metal having a higher melting point than the maximumtemperature of the heater unit 200.

The heater holding arm 520 is extendable in an approximately horizontaldirection and connected to the heater holding ring 510 at one end. Theother end of the heater holding arm 520 is supported by the verticalstand 540 in such a way that the position of the heater holding arm 520can be moved in an approximately vertical direction. The temperaturecontroller holding arm 530 holds the temperature controller 400.Alternatively, the temperature controller 400 may be held by the heaterholding arm 520 or may be placed in the material testing machine 800,without using the temperature controller holding arm 530.

The vertical stand 540 is, for example, a round bar extending in avertical direction and supports the heater holding arm 520 and thetemperature controller holding arm 530 in such a way that the heights ofthe heater holding arm 520 and the temperature controller holding arm530 can be changed. This facilitates vertical adjustment of the heaterunit 200 to a desired part of the test specimen 700. The support base550 includes a leg portion having an approximately letter “U” shape, onwhich the vertical stand 540 is fixed.

By adjusting the horizontal location of the support base 550, the heaterholding unit 500 can be easily moved to a set position for heating thetest specimen 700 held in the material testing machine 800. In otherwords, the heater unit 200 can be brought to the set position relativeto the test specimen 700 held in the material testing machine 800 byadjusting the horizontal location of the support base 550 and adjustingvertical and horizontal positions of the heater holding arm 520. In thefollowing description, the “set position” refers to a position of theheater unit 200 set for heating the test specimen 700 held in thematerial testing machine 800 and in which the test specimen 700 isapproximately aligned with the axis of the heater unit 200.

The temperature controller 400 includes a controller main unit 410, adisplay 420, operation buttons 430, a power cable 440, and a connectioncable 450. The display 420 displays a set temperature (targettemperature), a measured temperature of the test specimen 700, and thelike. The operation buttons 430 receive an operator's input and set atarget temperature and the like. Electric power is supplied through thepower cable 440. The connection cable 450 is used to supply electricpower to the heater unit 200 for heating the test specimen 700 and tosend an output signal from the thermocouple sensor 310 to thetemperature controller 400. The temperature controller 400 will bedescribed in detail below.

The thermal insulation unit 600 includes a pair of heat insulators 610,belts 620, and locks 630. The heat insulators 610 are, for example, madeof a high-temperature thermal insulation material such as zirconia fiberor alumina fiber or the like. The heat insulators 610 are, for example,two semi-cylindrical members that are linked together at one end in sucha way that the thermal insulation unit 600 can open and close. Each heatinsulator 610 has recessed portions in such a way that when the heatinsulators 610 are put together, spaces are formed inside the thermalinsulation unit 600 for accommodating the heater unit 200, the testspecimen 700, and the like.

The belts 620 are arranged at upper and lower sides of circumferences ofthe heat insulators 610 and are configured in such a way that two endsof each belt 620 are connected together with the lock 630. When thethermal insulation unit 600 is closed, the heater unit 200 and the testspecimen 700 are covered by the heat insulators 610. This enables toprevent or reduce humidity and airflow from entering between the testspecimen 700 and the heater unit 200, reducing heat loss and energyconsumption during the heating.

Alternatively, the locks 630 may be communicably connected to thetemperature controller 400 with a wired or wireless connection to allowthe temperature controller 400 to control locking and unlocking of thelocks 630. For example, the temperature controller 400 may controls thelocks 630 in such a way that the locks 630 locks a closed state of thethermal insulation unit 600 when the temperature of the test specimen700 exceeds a predetermined temperature and unlocks the closed statewhen the temperature of the test specimen 700 falls below thepredetermined temperature at the end of a test. Here, the predeterminedtemperature is a safe temperature for handling the test specimen 700.Such locking control prevents an operator from opening the thermalinsulation unit 600 when the temperature of the test specimen 700 isstill high, preventing from getting burn by touching the test specimen700 by mistake.

The heat insulators 610 are not limited to two semi-cylindrical membersthat are linked together at one end, and may be any other structure thatopens and closes for uncovering and covering the heater unit 200 afterthe heater unit 200 is placed in the material testing machine 800 forheating the test specimen 700.

FIG. 3 is a partial-sectional view of the heater unit 200 of thespecimen heating apparatus 100 according to the first embodiment. Theheater unit 200 includes a plurality of ceramic insulators 210, aplurality of heating elements 220, a metallic housing 230, and a heaterpower terminal (not illustrated). The ceramic insulator 210 has astick-like shape extending lengthways and an arc-like cross section. Theplurality of ceramic insulators 210 are put together side by side toform an approximately letter “C” shape whose opening is positioned onthe right-hand side when viewed from the above.

In each ceramic insulator 210, a plurality of heating element holes 211is formed so as to penetrate through the ceramic insulator 210. Theheating element 220 is inserted continuously through the heating elementholes 211 of the plurality of ceramic insulators 210 that are puttogether to form an approximately letter “C” shape, thereby forming acylindrical heat generating unit. Here, the plurality of ceramicinsulators 210 are linked together with the heating elements 220penetrating therethrough in such a way that the plurality of ceramicinsulators 210 is collectively swingable and forms an opening that isallowed to open and close for receiving the test specimen 700 while thetest specimen 700 is being held by the specimen grips 820. The heatingelement 220 has a helix wound resistance coil and is, for example, madeof a nickel-chromium alloy or the like. Alternatively, the heatingelement 220 may have an elongated sheet-like shape. The maximumtemperature of the heater unit 200 is, for example, 500-700° C.

The metallic housing 230 is made of a metal plate such as a stainlesssteel plate and the like, and includes a cylindrical cover portion 231,a plurality of end cover portions 232, opening cover portions 233, andfastening portions 234. The cylindrical cover portion 231 covers anapproximately cylindrical outer surface formed by the combined ceramicinsulators 210. The end cover portions 232 each have an approximatelyinverse letter “U” shape. The end cover portions 232 protrude from theupper end and the lower end of the cylindrical cover portion 231 and arebended toward the axial center of the heater unit 200, thereby coveringboth upper and lower end surfaces of the ceramic insulators 210 andpreventing the ceramic insulators 210 from moving up or down. A thermalinsulation layer may be added between the cylindrical cover portion 231and the ceramic insulators 210. The additional thermal insulation layerenables to reduce heat loss and facilitate heat concentration in theaxial center region.

The opening cover portion 233 covers part of the outer surface, the sidesurface, and part of the inner surface of the ceramic insulator 210 thatfaces the opening. The fastening portion 234 is a protrusion with afastening hole 235 and formed close to the opening so as to protrudeoutward. To close the opening, a bolt is inserted through the fasteningholes 235 of the corresponding fastening portions 234 and tightened bytorquing a nut.

The specimen temperature measurement unit 300 is built into the heaterunit 200. The specimen temperature measurement unit 300 includes athermocouple sensor 310 and a sensor arm 320. The sensor arm 320 isformed of an elongated metal plate having elasticity, such as stainlesssteel plate or the like. The thermocouple sensor 310 is attached to oneend of the sensor arm 320, and the other end of the sensor arm 320 ismechanically secured on one of the end cover portions 232 formed on thelower end of the heater unit 200 by riveting. Further, the specimentemperature measurement unit 300 is placed inside the heater unit 200 insuch a way that the thermocouple sensor 310 faces the opening of theheater unit 200. The sensor arm 320 extends from the lower end of theheater unit 200 to the axial center of the heater unit 200 at an angleand holds the thermocouple sensor 310 at approximately the axial centerof the heater unit 200.

The connection cable 450 is separated into two cables in the vicinity ofthe lower end of the heater unit 200. One of these cables is connectedto a heater power terminal (not illustrated) for supplying electricpower to the heating elements 220, and the other cable is connected tothe thermocouple sensor 310 for sending an output signal from thethermocouple sensor 310.

In the present embodiment, the sensor arm 320 is mechanically secured onthe end cover portion 232. Alternatively, the sensor arm 320 may besecured by welding or may be secured on a part different from the endcover portion 232. Further, the end cover portion 232 may be extended,and uses the extended part as the sensor arm 320.

FIG. 4 is a perspective view of the heater unit 200 of the specimenheating apparatus 100 according to the first embodiment placed forheating the test specimen 700 held in the material testing machine 800.In FIG. 4, the heater unit 200 is held by the heater holding ring 510 insuch a way that the heater unit 200 surrounds the test specimen 700gripped between the specimen grips 820. To set the heater unit 200 inposition, first, the opening of the heater unit 200 is widened, and thetest specimen 700 is allowed to move into the heater unit 200 throughthe opening. Subsequently, the heater unit 200 is closed using the boltsand nuts. Then, the heater holding ring 510 is connected to hold theclosed heater unit 200 at the set position relative to the test specimen700 for heating.

FIG. 5 is a schematic cross-sectional view of the heater unit 200covered with the thermal insulation unit 600 according to the firstembodiment, which is placed for heating the test specimen 700 held bythe specimen grips 820. When the test specimen 700 is received throughthe opening of the heater unit 200 and the heater unit 200 is brought tothe set position, the thermocouple sensor 310, which is attached to theone end of the sensor arm 320 and placed opposite the opening, comesinto contact with and is pressed against the test specimen 700, causingdeflection in the sensor arm 320. This ensures that the thermocouplesensor 310 is securely in contact with the test specimen 700 foraccurate temperature measurement.

FIG. 6 is a schematic block diagram of the temperature controller 400 ofthe specimen heating apparatus 100 according to the first embodiment.The temperature controller 400 includes, as described above, thecontroller main unit 410 including the display 420 and the operationbuttons 430, the power cable 440, and the connection cable 450. Thecontroller main unit 410 further includes a controller 460, a powersupply 470, a relay 480, and a temperature signal processing unit 490.

The display 420, the operation buttons 430, the power supply 470, therelay 480, and the temperature signal processing unit 490 are connectedto the controller 460. The relay 480 is, for example, a solid-staterelay (SSR) which is an electronic on-off switching device that actslike an electromechanical relay yet has no movable contacts. The relay480 receives a control signal from the controller 460 and turns on andoff the supply of electric power to the heater unit 200 in response tothe received control signal.

When a target temperature is set by using the display 420 and theoperation buttons 430, the controller 460 sends a control signal to therelay 480 to control turning-on and turning-off of the electric powersupply to the heater unit 200 via the connection cable 450.Specifically, the specimen temperature measurement unit 300 abutting thetest specimen 700 outputs a signal representing a measured temperatureof the test specimen 700 to the temperature signal processing unit 490.The temperature signal processing unit 490 is configured to receive theoutput signal from the thermocouple sensor 310 and convert the receivedoutput signal to a temperature signal, and sends the temperature signalto the controller 460. The controller 460 causes the display 420 todisplay the measured temperature of the test specimen 700 and maintainsthe temperature of the test specimen 700 at the target temperature byusing feedback control.

FIG. 7 is a diagram illustrating an exemplary feedback loop for thecontroller 460 of the temperature controller 400. The controller 460 is,for example, a Proportional-Integral-Derivative (PID) controller thatuses a control loop feedback mechanism, as illustrated in FIG. 7. ThePID controller is used to control the temperature of the heater unit 200by controlling the electric power supply through the relay 480. The PIDcontroller controls the temperature by applying the correction on thecalculated error value e(t) of the difference between the targettemperature and the temperature measured with the thermocouple sensor310.

According to the present embodiment, a specimen heating apparatus 100having a simpler structure is provided. The specimen heating apparatus100 is a low-cost and highly efficient heating apparatus capable ofheating the test specimen 700 to high temperature. The heater holdingunit 500 enables fine adjustment of the position of the heater unit 200relative to the test specimen 700. Thus, the specimen heating apparatus100 is easy to install in various material testing machines.

Second Embodiment

A specimen heating apparatus according to the second embodiment isdescribed with reference to FIG. 8 to FIG. 10. FIG. 8 is a schematicperspective view of a heater unit 200 a of a specimen heating apparatus100 a according to the second embodiment. FIG. 9 is a schematicperspective view of the heater unit 200 a that is placed for heating thetest specimen 700 held in the material testing machine 800. FIG. 10 is aschematic block diagram of the specimen heating apparatus 100 a.

In the present embodiment, the specimen heating apparatus 100 a includesthe heater unit 200 a, a specimen temperature measurement unit 300 a,the temperature controller 400 a, heater holding units 500 a, and thethermal insulation unit 600 a, as illustrated in FIG. 10.

The heater unit 200 a according to the present embodiment is differentfrom that of the first embodiment in the following two points. First, inthe first embodiment, the heater holding unit 500 and the heater unit200 are made as different components and connected by the heater holdingring 510. Whereas, in the present embodiment, the heater holding unit500 a is incorporated into the heater unit 200 a for holding the heaterunit 200 a in the set position relative to the test specimen 700. Theheater holding unit 500 a is described in detail below. Second, atemperature sensor attachment hole 240 is formed on the side surface ofthe heater unit 200 a. The temperature sensor attachment hole 240 is athrough-hole for installing a non-contact temperature sensor 330 thatmeasures the surface temperature of the test specimen 700. Thenon-contact temperature sensor 330 replaces the thermocouple sensor 310of the first embodiment. The non-contact temperature sensor 330 isdescribed in detail below.

The heater holding unit 500 a of the heater unit 200 a is now describedin detail with reference to FIG. 8 and FIG. 9. The heater holding unit500 a includes a plurality of tongue-like projections 560 continuouslyextending from all or part of the end cover portions 232 formed at theupper end and the lower end of the metallic housing 230. Eachtongue-like projection 560 has an equal length and projects toward theaxial center of the heater unit 200 a at an angle. The tongue-likeprojections 560 are made of the same material as the end cover portions232 and the metallic housing 230, which is made of a metal plate such asa stainless steel plate or the like.

The overall length of the heater unit 200 a including two heater holdingunits 500 a formed at the upper end and the lower end of the heater unit200 is approximately equal to the gauge length of the test specimen 700to be tested. In other words, an axial distance from top part of theplurality of tongue-like projections 560 formed on the upper end of theheater unit 200 a to top part of the plurality of tongue-likeprojections 560 formed on the lower end of the heater unit 200 a isapproximately equal to the length of the gauge section of the testspecimen 700 to be tested. This enables the plurality of tongue-likeprojections 560 to come into contact with the test specimen 700 atlocations between the gauge section and the shoulders and enables theheater unit 200 a including two heater holding units 500 a to fitbetween the shoulders of the test specimen 700.

When the heater unit 200 a is set in the material testing machine 800for heating the test specimen 700, the plurality of tongue-likeprojections 560 enables the heater unit 200 a to be self-aligned withthe test specimen 700 and held securely in the set position relative tothe test specimen 700. This is because all of the tongue-likeprojections 560 project toward the axial center of the heater unit 200a, thereby the heater unit 200 a is coaxially self-aligned with the testspecimen 700. Further, because the plurality of tongue-like projections560 is flexible and generate holding force as a whole when the pluralityof tongue-like projections 560 is pressed against the test specimen 700and the top part of each tongue-like projection 560 bows outward. Thisprevents the heater unit 200 a from sliding up or down.

The tongue-like projection 560 may alternatively be formed as a separatemember and then welded or mechanically secured by riveting on the endcover portion 232. The tongue-like projection 560 may also be secured toa location other than the end cover portion 232. According to thepresent embodiment, the heater holding unit 500 a can be significantlysimplified compared with that of the first embodiment illustrated inFIG. 2. The shape of a top end portion of the tongue-like projection 560may be changed depending on the cross-sectional shape of the testspecimen 700 for better fitting. This enables the specimen heatingapparatus 100 a to be compatible with different types of test specimens.

The non-contact temperature sensor 330 is now described in detail withreference to FIG. 8 and FIG. 9. In the present embodiment, the specimentemperature measurement unit 300 a includes the non-contact temperaturesensor 330 and a padding 340 covering the non-contact temperature sensor330. The non-contact temperature sensor 330 is, for example, a surfacetemperature sensor such as an infrared temperature sensor. The padding340 is made of a high-temperature thermal insulation material. Theoverall diameter of the non-contact temperature sensor 330 covered bythe padding 340 is approximately equal to the diameter of thetemperature sensor attachment hole 240.

When the non-contact temperature sensor 330 is installed in the heaterunit 200 a, the non-contact temperature sensor 330 measures infraredrays radiated from the surface of the test specimen 700. The temperaturesensor attachment hole 240 is arranged in such a way that thenon-contact temperature sensor 330 covered with the padding 340 pointsdirectly to the test specimen 700 when the heater unit 200 a is broughtto the set position for heating.

As illustrated in FIG. 10, the temperature controller 400 a includes thedisplay 420, the operation buttons 430, the power cable 440, and aconnection cable 450 a, the controller 460, the power supply 470, therelay 480, and a temperature signal processing unit 490 a. Theconnection cable 450 a is used to supply electric power to the heaterunit 200 a for heating the test specimen 700 and to send an outputsignal from the non-contact temperature sensor 330 to the temperaturesignal processing unit 490 a. The temperature signal processing unit 490a is configured to receive the output signal from the non-contacttemperature sensor 330 and convert the received output signal into atemperature signal.

The thermal insulation unit 600 a is the same as the thermal insulationunit 600 of the first embodiment except that the space formed inside thethermal insulation unit 600 a is modified so as to accommodate theplurality of tongue-like projections 560 formed at the upper end and thelower end of the heater unit 200 a.

According to the present embodiment, the tongue-like projections 560enables the heater unit 200 a to stay in position and to be aligned withthe test specimen 700 gripped between the specimen grips 820 of thematerial testing machine 800, and the non-contact temperature sensor 330installed on the side of the heater unit 200 enables to measure thereal-time surface temperature of the test specimen 700 without the needfor any physical contact.

Third Embodiment

FIG. 11 is a schematic cross-sectional view of a specimen heatingapparatus 100 b according to the third embodiment, which is placed forheating the test specimen 700 held between the specimen grips 820 of thematerial testing machine 800. The specimen heating apparatus 100 bincludes the heater unit 200 a, the specimen temperature measurementunit 300 a, the temperature controller (not illustrated), the heaterholding unit 500 a, and a thermal insulation unit 600 b. The heater unit200 a, the specimen temperature measurement unit 300 a, the temperaturecontroller, and the heater holding unit 500 a are the same as those inthe second embodiment. The specimen heating apparatus 100 b of thepresent embodiment further includes a pair of detachable auxiliaryheaters 250 and a pair of detachable cooling units 900. The thermalinsulation unit 600 b is modified from the thermal insulation unit 600 aof the second embodiment so as to accommodate the additional auxiliaryheaters 250.

The auxiliary heater 250 is a band heater attached to each specimen grip820 for heating the test specimen 700 from its shoulder, which isgripped by the specimen grip 820. The auxiliary heaters 250 are poweredand controlled by the temperature controller, as in the heater unit 200a. Heating the specimen grips 820 with the auxiliary heaters 250shortens time to reach the target temperature at the test specimen 700and assists in maintaining the target temperature of the test specimen700.

In this case, however, part of the heat generated by the auxiliaryheater 250 may escape through the connecting rod 830 to the main frame810 of the material testing machine 800. In the present embodiment, inorder to prevent or reduce such heat loss, the detachable cooling unit900 is installed at the base of each connecting rod 830. The coolingunit 900 cools the connecting rod 830 to reduce the heat transferthrough the connecting rod 830 and reduces a temperature rise in themain frame 810 of the material testing machine 800. The cooling unit 900includes a cooler 910, a feed water tube 920, a drain tube 930,attachment belts 940, and a feed water supply (not illustrated). Coldwater is supplied to the cooler 910 through the feed water tube 920, andhot water heated at the base of the connecting rod 830 is drained fromthe drain tube 930. The cooler 910 is secured to the main frame 810 ofthe material testing machine 800 by the attachment belts 940.Alternatively, the cooler 910 may be secured to another part of thematerial testing machine 800, through which major part of the heatgenerated by the auxiliary heater 250 is transferred.

The feed water supply of the cooling unit 900 may be communicablyconnected to the temperature controller 400 a using a wired or wirelessconnection, and the temperature controller 400 a may control the outputof the feed water supply in response to the measured temperature of thetest specimen 700. For example, to facilitate cooling down of the testspecimen 700 after testing, the temperature controller 400 a mayincrease the feed water output after the heating of the test specimen700 stops at the end of a test and maintains the increased feed wateroutput until the measured temperature of the test specimen 700 fallsbelow a predetermined temperature. Such temperature control by thetemperature controller 400 a after the end of a test may also beperformed together with the locking control of the locks 630. Thisfurther improves safety of the operation at high temperatureenvironment.

According to the present embodiment, the specimen heating apparatus 100b can heat up the test specimen 700 faster without damaging the materialtesting machine 800.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of this disclosure. For example, in the foregoingembodiments, the specimen heating apparatus is described for use in thematerial testing machine performing tensile testing. However, thespecimen heating apparatuses according to the present disclosure mayalso be used in other mechanical tests.

The invention claimed is:
 1. A specimen heating apparatus for a materialtesting machine, comprising: a heater unit configured to heat a testspecimen held in the material testing machine for mechanical strengthtesting wherein the heater unit comprises a plurality of ceramicinsulators, a plurality of heating elements, and a metallic housing,wherein the heater unit is cylindrical and configured tocircumferentially enclose the test specimen; a heater holding unitconfigured to hold the heater unit in a set position relative to thetest specimen for heating the test specimen held in the material testingmachine wherein the heater holding unit includes a top plurality oftongue-like projections formed on an upper end of the heater unit, thetop plurality of tongue-like projections each extending upwards towardan axial center of the heater unit and a bottom plurality of tongue-likeprojections formed on a lower end of the heater unit, the bottomplurality of tongue-like projections each extending downwards toward anaxial center of the heater unit; a specimen temperature measurement unitattached to the heater unit and configured to measure temperature of thetest specimen when the heater unit is in the set position wherein thespecimen temperature measurement unit comprises a thermocouple sensorand a sensor arm, the sensor arm being attached to the heater unit atone end and to the thermocouple sensor at another end; a temperaturecontroller configured to control heating of the heater unit in responseto a temperature measured by the specimen temperature measurement unit;and a thermal insulation unit configured to cover the heater unit. 2.The specimen heating apparatus of claim 1, wherein each ceramicinsulator extends lengthways and has an equal length, wherein eachheating element penetrates through inside the plurality of the ceramicinsulators, wherein the metallic housing is configured to hold theplurality of ceramic insulators so that the plurality of ceramicinsulators is swingable and forms an opening that is allowed to beopened and closed for receiving the test specimen.
 3. The specimenheating apparatus of claim 2, wherein the heater unit further includes aheat insulator arranged between the plurality of ceramic insulators andthe metallic housing.
 4. The specimen heating apparatus of claim 1,wherein the sensor arm is made of a flexible material and arrangedinside the heater unit opposite the opening in such a way that, when theheater unit is brought to the set position, the thermocouple sensorattached to the sensor arm comes in contact with the test specimen andthe test specimen deflects the sensor arm upon contact.
 5. The specimenheating apparatus of claim 1, wherein the specimen temperaturemeasurement unit includes a non-contact temperature sensor installed ina through-hole formed on a side surface of the heater unit.
 6. Thespecimen heating apparatus of claim 5, wherein the specimen temperaturemeasurement unit further includes a heat insulating padding covering thenon-contact temperature sensor, and wherein the non-contact temperaturesensor covered with the heat insulating padding is inserted into thethrough-hole formed on the side surface of the heater unit.
 7. Thespecimen heating apparatus of claim 6, wherein the through-hole formedon the side surface of the heater unit is arranged in such a way thatthe non-contact temperature sensor, which is covered with the heatinsulating padding and inserted into the through-hole, points the testspecimen when the heater unit is in the set position.
 8. The specimenheating apparatus of claim 1, wherein the heater holding unit includes aheater holding ring for holding the heater unit, a heater holding armconnected to the heater holding ring and configured to be extendable ina horizontal direction, a vertical stand configured to hold the heaterholding arm in such a way that a holding location of the heater holdingarm is movable in a vertical direction, and a support base on which thevertical stand is secured.
 9. The specimen heating apparatus of claim 1,wherein an axial distance from a top part of the top plurality oftongue-like projections to a top part of the bottom plurality oftongue-like projections is equal to length of a gauge section of thetest specimen.
 10. The specimen heating apparatus of claim 1, whereinwhen the heater unit is in the set position, the top plurality oftongue-like projections comes into contact with the test specimen atlocations between a gauge section and shoulders of the test specimen.